Group III nitride-based compound semiconductor device

ABSTRACT

A characteristic feature of the invention is to form, in a Group III nitride-based compound semiconductor device, a negative electrode on a surface other than a Ga-polar C-plane. In a Group III nitride-based compound semiconductor light-emitting device, there are formed, on an R-plane sapphire substrate, an n-contact layer, a layer for improving static breakdown voltage, an n-cladding layer made of a multi-layer structure having ten stacked sets of an undoped In 0.1 Ga 0.9 N layer, an undoped GaN layer, and a silicon (Si)-doped GaN layer, a multi-quantum well (MQW) light-emitting layer made of a combination of In 0.25 Ga 0.75 N well layers and GaN barrier layers stacked alternatingly, a p-cladding layer made of a multi-layer structure including a p-type Al 0.3 Ga 0.7 N layer and a p-In 0.08 Ga 0.92 N layer, and a p-contact layer (thickness: about 80 nm) made of a stacked structure including two p-GaN layers having different magnesium concentrations. Through etching, the n-contact layer having a thickness direction along the c-axis is provided with stripe-patterned microditches each having side walls, which assume a C-plane, whereby ohmic contact is established between a negative electrode and each C-plane side wall.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a Group III nitride-based compoundsemiconductor device having a characteristic shape of an n-type regionwhere a negative electrode has been provided. As used herein, the term“Group III nitride-based compound semiconductor” encompasses asemiconductor represented by the formula Al_(x)Ga_(y)In_(1-x-y)N (0≦x≦1,0≦y≦1, 0≦x+y≦1); such a semiconductor containing a predetermined elementso as to attain, for example, an n-type/p-type conduction; and such asemiconductor in which a portion of a Group III element is substitutedby B or Tl, and a portion of the Group V element is substituted by P,As, Sb, or Bi.

2. Background Art

In the development of Al_(x)Ga_(y)In_(1-x-y)N semiconductors,crystallinity of the semiconductor has been enhanced, and conductivitythereof has been well-controlled, leading to production of a variety ofsemiconductor devices such as light-emitting diodes, laser diodes, andHEMTs. Currently, in a typical production process for semiconductordevices, a plurality of Group III nitride-based compound semiconductorlayers are formed through epitaxial growth on a C-plane or A-planesapphire substrate, silicon substrate, or SiC substrate. In many cases,when such Group III nitride-based compound semiconductor epitaxiallayers are formed on the aforementioned hetero-substrate, the growthsurface of epitaxial growth is a C-plane such that the thickness of eachGroup III nitride-based compound semiconductor layer increases along thec-axis. Also, when epitaxial growth is performed on a GaN thick layerhaving a C-plane as a main plane and serving as a growth substrate, thegrowth surface of an epitaxial is a C-plane such that the thickness ofthe epitaxial film increases along the c-axis.

Meanwhile, when the thickness direction of a GaN substrate is the c-axisdirection, one surface normal to the c-axis is a Ga-polar surface, andthe other surface is an N-polar surface. The Ga-polarity is thedirection of the vector from the Ga atom to the nitrogen atom between Gaand nitrogen atoms which are connected with each other parallel toc-axis. Whereas the nitrogen-polarity is the direction of the vectorfrom the nitrogen atom to the Ga atom between nitrogen and Ga atomswhich are connected with each other parallel to c-axis. Accordingly,Ga-polar surface is defined as the surface whose normal vector orientedto the outside is equal to the Ga-polarity. Whereas nitrogen-polarsurface is defined as the surface whose normal vector oriented to theoutside is equal to the nitrogen-polarity.

When GaN is epitaxially grown on the aforementioned hetero-substratesuch that the C-plane is a growth surface, the uppermost layer of theepitaxial film assumes a Ga-polar surface. When a C-plane GaN substrateis employed and GaN is epitaxially grown on the Ga-polar surface, theuppermost layer of the epitaxial film assumes a Ga-polar surface.However, those skilled in the art know that when epitaxial growth isperformed on the N-polar surface of the GaN substrate through MOVPE orhalide VPE, an epitaxial film having high crystallinity cannot beformed.

In the case where the thickness direction of a Group III nitride-basedcompound semiconductor layer is the c-axis direction and a plurality ofsuch semiconductor layers are stacked, the interface between two layersassumes C-plane. In this case, the following problem is known to arisein an HEMT or a light-emitting device having an MQW light-emittinglayer.

In an HEMT having a two-dimensional electron gas layer provided betweenan InAlGaN layer and an n⁻-type GaN layer, when the polarization of theInAlGaN layer is greater than that of GaN and each interlayer interfaceassumes C-plane, electrons tend to be accumulated in a hetero-interface.Thus, in this case, device characteristics of interest may fail to beattained. For example, normally-off cannot be attained.

When a Group III nitride-based compound semiconductor is formed on asapphire substrate having R-plane ((1-102) plane) as a main plane suchthat A-plane ((11-20) plane); i.e., a non-polar surface, of thesemiconductor serves as a growth surface, a polarization fieldperpendicular to a hetero-interface is not formed. In this case,generally, a normally-off transistor can be produced, and electrons canrun without being affected by a polarization field, which isadvantageous in high-speed operation.

In relation to light-emitting devices, there has been proposed aso-called type-II quantum well active layer, which is an MQWlight-emitting layer (active layer) in which electrons are quantumizedand confined in one layer, and holes in another layer. When a type-IIquantum well active layer is provided on a non-polar surface such asnon-polar A-plane ((11-20) plane), the active layer is not affected bypolarization, and high light emission efficiency is realized.

Thus, recently, a A-plane GaN substrate or a M-plane GaN substrate havebeen commercialized, and devices in which a Group III nitride-basedcompound semiconductor layer having a thickness direction of the a-axisor m-axis (i.e., non-polar axis) direction is provided on such a GaNsubstrate have become of interest.

Japanese Patent Application Laid-Open (kokai) No. 2007-43164 disclosesthat an electrode is difficult to form on the N-polar surface of ann-type GaN substrate, which is opposite the Ga-polar surface on which adevice has been provided.

SUMMARY OF THE INVENTION

Even though an electrode, for example, a Ti/Al double-layer electrode,is formed on a non-polar A-plane or M-plane of Group III nitride-basedcompound semiconductor, an ohmic electrode cannot easily be formed, ascompared with formation on a Ga-polar C-plane. Actually, a Ti/Al ohmicelectrode can be formed on a Ga-polar C-plane through heating at 500 to600° C., whereas heating at 700 to 900° C. is required for forming aTi/Al ohmic electrode on an A-plane or M-plane. When such hightemperature is applied to devices, device characteristics may beimpaired.

In view of the foregoing, an object of the present invention is to forma negative electrode, through heating at relatively low temperature, inan n-type region having a main plane which is a non-polar A-plane orM-plane of a GaN substrate; which is an N-polar C-plane of a GaNsubstrate; or which is a plane other than a Ga-polar C-plane.

Accordingly, in a first aspect of the present invention, there isprovided a Group III nitride-based compound semiconductor deviceproduced through epitaxial growth of a Group III nitride-based compoundsemiconductor and having an n-type region provided with a negativeelectrode; wherein the n-type region is defined by a surface of ann-type Group III nitride-based compound semiconductor layer formedthrough epitaxial growth and has one or more surfaces which are notparallel to the c-axis and which are formed through etching on saidsurface assuming the main plane other than a Group-III-element-polarC-plane.

In a second aspect of the present invention, there is provide a GroupIII nitride-based compound semiconductor device produced throughepitaxial growth of a Group III nitride-based compound semiconductor andhaving an n-type region provided with a negative electrode; wherein then-type region is defined by a surface of an n-type Group IIInitride-based compound semiconductor substrate, said surface assuming anA-plane or M-plane as its main plane, and are provided with surfaceswhich are not parallel to the c-axis and which are formed throughetching.

As used herein, the term “Group-III-element-polar” refers to Ga-polar inthe case of GaN. In the cases of mixed crystals or other semiconductors,Group III element atoms are present at the surface of a layer and areeach bonded to three nitrogen atoms present in the layer or a substrate.According to the first aspect, when the n-type region is defined by asurface of a Group III nitride-based compound semiconductor film formedthrough epitaxial growth, the plane of the n-type region assumes a planeother than a Group-III-element-polar C-plane. The term “a plane otherthan a Group-III-element-polar C-plane” refers to an N-polar C-plane ora plane other than a C-plane. In the plane, other surfaces which are notparallel to the c-axis are formed through etching. The term “a surfacewhich is not parallel to the c-axis” refers to, for example, a surfaceassuming a plane other than an A-plane or an M-plane. Most preferably, asurface which is perpendicular to the c-axis; i.e., a surface assuming aC-plane, is exposed. According to the second aspect, when the n-typeregion is defined by a main plane of a Group III nitride-based compoundsemiconductor substrate, the main plane assumes an A-plane or M-plane.In the A-plane or M-plane, other surfaces which are not parallel to thec-axis are formed through etching.

The surfaces which are parallel to the c-axis are, for example, surfacesassuming an A-plane or an M-plane. Thus, in the present invention, thesurfaces which are not parallel to the c-axis mean surfaces assuming aC-plane or slanted surfaces tilted with respect to the epitaxial growthsurface. The slanted surface is represented by indices (a₁a₂a₃c),wherein c is not 0. The most preferred surface is a C(0001) surface.When the surface is other than a surface assuming a C-plane, a surfacehaving a larger value of “c” is preferred. The angle between the normalline of the surface and the c-axis is ideally 0°, preferably 45° orlower, more preferably 30° or lower, still more preferably 15° or lower.When the angle falls within the above ranges, Ga-polarity predominatesat the exposed surface. In other words, the gist of the presentinvention resides in that a negative electrode is not directly formed onan A(11-20) plane or an M(1-100) plane, but is formed through providing,through etching in advance, a surface assuming C-plane or a surfacewhich does not assume at least an A-plane or an M-plane. When a negativeelectrode is formed on a slanted surface such as a (11-22) surface or a(11-24) surface; i.e., “a semi-polar surface,” according to the presentinvention, a surface having characteristics more similar to those ofC-plane is formed through etching. For example, the C-plane can beexposed through weak etching of an epitaxial film having a small offangle from the C-plane, although the C-plane has high etchingresistance.

A third aspect of the present invention is drawn to a specificembodiment of the device according to the first aspect, wherein then-type region provided with the negative electrode is defined by asurface of the semiconductor layer assuming an A-plane as its mainplane, and at least a Group-III-element-polar C-plane region formedthrough etching is exposed to the negative electrode, i.e., contactedwith the negative electrode.

A fourth aspect of the present invention is drawn to a specificembodiment of the device according to the second aspect, wherein atleast a Group-III-element-polar C-plane region formed through etching isexposed to the negative electrode, i.e., contacted with the negativeelectrode, formed on a surface of the n-type Group III nitride-basedcompound semiconductor substrate, said surface assuming an A-plane orM-plane as its main plane.

A fifth aspect of the present invention is drawn to a specificembodiment of the device according to the first or third aspect, whereinthe Group III nitride-based compound semiconductor is epitaxially grownon a sapphire substrate having an R-plane plane as its main plane. TheGroup III nitride-based compound semiconductor grown in the R-plane ofthe sapphire substrate has an A-plane growth surface, with the a-axisbeing the axis of growth.

A sixth aspect of the present invention is drawn to a specificembodiment of the device according to the preceding aspects, wherein thenegative electrode is provided through sequentially forming, throughvapor deposition, a first metal layer containing at least titanium (Ti)or vanadium (V), and a second metal layer containing at least aluminum(Al).

The negative electrode provided on a surface of a Group IIInitride-based compound semiconductor other than a surface assuming aGroup-III-element-polar C-plane is difficult to form as an ohmicelectrode. Thus, in the formation of a negative electrode on a surfaceof a Group III nitride-based compound semiconductor other than a surfaceassuming a Group-III-element-polar C-plane, a surface havingcharacteristics more similar to those of C-plane is formed. As a result,the exposed surface exhibits Group-III-element-polarity, and thenegative electrode can serve as an ohmic electrode through heating atrelatively low temperature.

This technique is advantageous particularly when a negative electrode isformed on an A-plane or M-plane, which is a surface parallel to thec-axis of the Group III nitride-based compound semiconductor. Since thecrystal orientation of the epitaxial film can be identified by thecrystal orientation of the growth substrate, stripe-patternedmicroditches or a similar structure each having C-plane side walls canbe readily formed through etching. Each microditch has oppositely facingside walls, one of which is an N-polar surface and the other of which isa Ga-polar surface. Therefore, although the N-polar side-surface isexposed, i.e., contacted with the negative electrode, the other exposedGa-polar side-surface, i.e., contacted with the negative electrode,exhibits the effect of the invention. A portion of the negativeelectrode which is in contact with the Ga-polar C-plane readily providesan ohmic electrode through heating at comparatively low temperature.

The present invention is also advantageous, when a negative electrode isformed on a surface of Group III nitride-based compound semiconductorother than a surface assuming the A-plane or M-plane, for example; on anN-polar C-plane. According to the present invention, a surface on whichan ohmic electrode can be more readily formed as compared with anun-etched surface is exposed through etching. In this case, the exposedsurface preferably has characteristics more similar to those of aGa-polar C-plane.

The present invention is also advantageous particularly when thenegative electrode is formed from a Ti/Al double-layer or from a metalmulti-layer including a Ti-containing layer and an Al-containing layer.For example, when the above negative electrode is formed on a Ga-polarC-plane of n-GaN, Ti forms TiN thin film through substitution by Gaatoms present at the surface of n-GaN. The thus-formed TiN thin film isthought to enhance the ohmic property. If the negative electrode isformed on a surface other than a surface assuming the Ga-polar C-plane,substitution of Ga by Ti is difficult, or TiN thin film does notcompletely cover the surface. For such reasons, the ohmic propertycannot be enhanced. Thus, through exposing a Ga-polar C-plane by etchingor forming a surface exhibiting higher Ga-polarity by etching, thenegative electrode formed from a metal multi-layer including aTi-containing layer and an Al-containing layer exhibits an enhancedohmic property. This technique is also applicable to mixed crystalsother than n-GaN.

Furthermore, this technique is also applicable to formation of anegative electrode from a V/Al double-layer or from a metal multi-layerincluding a V-containing layer and an Al-containing layer.

BRIEF DESCRIPTION OF THE DRAWINGS

Various other objects, features, and many of the attendant advantages ofthe present invention will be readily appreciated as the same becomesbetter understood with reference to the following detailed descriptionof the preferred embodiments when considered in connection with theaccompanying drawings, in which:

FIG. 1 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 100, which is an embodiment of thepresent invention;

FIG. 2 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 200, which is another embodiment ofthe present invention;

FIG. 3 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 300, which is still anotherembodiment of the present invention; and

FIG. 4 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 400, which is yet another embodimentof the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A characteristic feature of the present invention resides in that when anegative electrode is formed on a surface other than a surface assuminga Group-III-element-polar C-plane, a surface exhibiting higherGa-polarity, most preferably a surface assuming C-plane, is exposedthrough etching. No particular limitation is imposed on the structureand characteristics of the semiconductor device to which the presentinvention is applied, so long as the above characteristic feature ismaintained.

It is not always difficult to form a C-plane through etching in asurface other than a surface assuming a Group-III-element-polar C-plane.When the epitaxial growth surface assumes an A-plane or M-plane, theC-plane orientation of the Group III nitride-based compoundsemiconductor layer can be identified from the orientation flat of thesubstrate employed. For example, when a stripe-shape mask is formed, thelongitudinal direction of the stripe is caused to adjust to be parallelto the C-plane of the Group III nitride-based compound semiconductorlayer; i.e., to be perpendicular to the c-axis. Then, microditches areformed through dry etching so that they are perpendicular to the A-planeor M-plane serving as a growth surface and parallel to the C-plane. Bothside walls of each microditch assume the C-plane of the Group IIInitride-based compound semiconductor layer, although one of the sidewalls which is an N-polar surface, the other is a Ga-polar surface.Therefore, ohmic contact between the electrode and the semiconductor canbe enhanced by the mediation of the Ga-polar surface.

Embodiment 1

FIG. 1 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 100, which is one embodiment of thepresent invention. The Group III nitride-based compound semiconductorlight-emitting device 100 has the following Group III nitride-basedcompound semiconductor layers stacked through epitaxial growth on anR-plane sapphire substrate 10. The thickness direction of each layercoincides with the a-axis direction. Specifically, a buffer layer (notillustrated, thickness: about 15 nm) formed of aluminum nitride (AlN) isprovided on the R-plane sapphire substrate 10, and an n-contact layer 11(thickness: about 4 μm) made of silicon (Si)-doped GaN is formed on thebuffer layer. On the n-contact layer 11, a layer 110 for improvingstatic breakdown voltage is formed from a stacked structure including anundoped GaN layer (thickness: 300 nm) and a silicon (Si)-doped GaN layer(thickness: 30 nm). On the layer 110 for improving static breakdownvoltage, there is formed an n-cladding layer 12 (thickness: about 74 nm)made of a multi-layer structure having ten stacked sets of an undopedIn_(0.1)Ga_(0.9)N layer, an undoped GaN layer, and a silicon (Si)-dopedGaN layer.

On the n-cladding layer 12, there is provided a multi-quantum well (MQW)light-emitting layer 13 made of a combination of seven wellIn_(0.25)Ga_(0.75)N layers (thickness: about 3 nm) and GaN barrierlayers (thickness: 3 nm) stacked alternatingly. On the light-emittinglayer 13, a p-cladding layer 14 (thickness: about 33 nm) made of amulti-layer structure including a p-Al_(0.3)Ga_(0.7)N layer and ap-In_(0.08)Ga_(0.92)N layer is formed. On the p-cladding layer 14, thereis provided a p-contact layer 15 (thickness: about 80 nm) made of astacked structure including two p-GaN layers having different magnesiumconcentrations.

An optically transparent electrode 20 made of indium tin oxide (ITO) isformed on the p-contact layer 15, and a negative electrode 30 is formedon the exposed surface of the n-contact layer 11. The negative electrode30 is formed from a titanium (Ti) layer (thickness: about 20 nm) and analuminum (Al) layer (thickness: about 2 μm). An electrode pad 25 made ofgold (Au) alloy is formed on the optically transparent electrode 20.

The exposed surface of the n-contact layer 11 is provided withstripe-patterned microditches through etching. The stripe-patternedmicroditches 11 s each have side walls, which assume a C-plane of then-contact layer 11. The width of each microditch and the inter-ditchdistance are adjusted to 0.2 μm, and the depth of each ditch is adjustedto 1 μm. The stripe-patterned microditches are formed on the entirety ofthe region where the negative electrode 30 has been formed. Note thatthe microditch width, the inter-ditch distance, and the ditch depth maybe individually adjusted to desired values. By virtue of thethus-provided microditches, the negative electrode 30 having a Ti/Alstacked structure exhibits excellent ohmic contact with the C-plane sidewalls 11 s formed in the n-contact layer 11. The ohmic contact can bereadily attained particularly with the Ga-polar C-plane side walls. Inorder to form an ohmic negative electrode, the negative electrode 30 isannealed at 400 to 600° C. For example, heating at about 500° C. issufficient for realizing annealing.

Embodiment 2

FIG. 2 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 200, which is another embodiment ofthe present invention. The Group III nitride-based compoundsemiconductor light-emitting device 200 has the following Group IIInitride-based compound semiconductor layers stacked through epitaxialgrowth on an A-plane n-GaN substrate 120. The thickness direction ofeach layer coincides with the a-axis direction. Specifically, ann-contact layer 11 (thickness: about 4 μm) made of silicon (Si)-dopedGaN is formed on the A-plane n-GaN substrate 120. On the n-contact layer11, a layer 110 for improving static breakdown voltage is formed from astacked structure including an undoped GaN layer (thickness: 300 nm) anda silicon (Si)-doped GaN layer (thickness: 30 nm). On the layer 110 forimproving static breakdown voltage, there is formed an n-cladding layer12 (thickness: about 74 nm) made of a multi-layer structure having tenstacked sets of an undoped In_(0.1)Ga_(0.9)N layer, an undoped GaNlayer, and a silicon (Si)-doped GaN layer.

On the n-cladding layer 12, there is provided a multi-quantum well (MQW)light-emitting layer 13 made of a combination of seven wellIn_(0.25)Ga_(0.75)N layers (thickness: about 3 nm) and GaN barrierlayers (thickness: 3 nm) stacked alternatingly. On the light-emittinglayer 13, a p-cladding layer 14 (thickness: about 33 nm) made of amulti-layer structure including a p-type Al_(0.3)Ga_(0.7)N layer and ap-In_(0.08)Ga_(0.92)N layer is formed. On the p-cladding layer 14, thereis provided a p-contact layer 15 (thickness: about 80 nm) made of astacked structure including two p-GaN layers having different magnesiumconcentrations.

An optically transparent electrode 20 made of indium tin oxide (ITO) isformed on the p-contact layer 15, and a negative electrode 30 is formedon the back surface of the n-GaN substrate 120. The negative electrode30 is formed from a titanium (Ti) layer (thickness: about 20 nm) and analuminum (Al) layer (thickness: about 2 μm). An electrode pad 25 made ofgold (Au) alloy is formed on the optically transparent electrode 20.

The back surface of the n-GaN substrate 120 is provided withstripe-patterned microditches through etching. The stripe-patternedmicroditches 120 s each have side walls, which assume a C-plane of then-GaN substrate 120. The width of each microditch and the inter-ditchdistance are adjusted to 2 μm, and the depth of each ditch is adjustedto 5 μm. The stripe-patterned microditches are formed on the entirety ofthe region where the negative electrode 30 has been formed. Note thatthe microditch width, the inter-ditch distance, and the ditch depth maybe individually adjusted to desired values. By virtue of thethus-provided microditches, the negative electrode 30 having a Ti/Alstacked structure exhibits excellent ohmic contact with the C-plane sidewalls 120 s formed in the n-GaN substrate 120. The ohmic contact can bereadily attained particularly with the Ga-polar C-plane side walls. Inorder to form an ohmic negative electrode, the negative electrode 30 isannealed at 400 to 600° C. For example, heating at about 500° C. issufficient for realizing annealing.

Modification of Embodiment 2

In the Group III nitride-based compound semiconductor light-emittingdevice 200 shown in FIG. 2, when the A-plane n-GaN substrate 120 ischanged to an M-plane n-GaN substrate, the thickness direction of eachlayer coincides with the m-axis. The back surface of the M-plane n-GaNsubstrate is provided, through etching, with stripe-patternedmicroditches each having side walls, which assume a C-plane. In thiscase, the negative electrode can be annealed at about 500° C.

Embodiment 3

FIG. 3 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 300, which is still anotherembodiment of the present invention. The Group III nitride-basedcompound semiconductor light-emitting device 300 shown in FIG. 3 has thesame structure as that of the Group III nitride-based compoundsemiconductor light-emitting device 200 shown in FIG. 2, except that aC-plane n-GaN substrate 121 is employed instead of the A-plane n-GaNsubstrate 120. In this case, the epitaxial growth surface is a Ga-polarsurface, and the other surface where a negative electrode is formed isan N-polar surface. In this structure, rather than provision of surfacesperpendicular to the N-polar C-plane, a surface embossment is preferablyformed in the form of slanted surfaces 121 s. In FIG. 3, the slantingangle is adjusted to 45°.

The slanted surfaces may have a single slanting angle or differentvalues. In Embodiment 3, slanted surfaces assuming A-plane or M-planeshould not be exposed. Instead of forming an embossment; i.e., theslanted surfaces 121 s, the entire back surface of the substrate may beprocessed to provide a single slanted surface having an off-angle of,for example, 45° or ≦10°.

Modification of Embodiment 3

In the Group III nitride-based compound semiconductor light-emittingdevice 300 shown in FIG. 3, an A-plane or M-plane n-GaN substrate may beemployed instead of the C-plane n-GaN substrate 121. In thismodification, slanted surfaces assuming A-plane or M-plane should not beexposed. Instead of forming an embossment; i.e., the slanted surfaces121 s, the entire back surface of the substrate may be processed toprovide a single slanted surface having an off-angle of, for example,45° or ≦10°.

Embodiment 4

FIG. 4 is a cross-section of a Group III nitride-based compoundsemiconductor light-emitting device 400, which is still anotherembodiment of the present invention. The Group III nitride-basedcompound semiconductor light-emitting device 400 shown in FIG. 4 has thesame structure as that of the Group III nitride-based compoundsemiconductor light-emitting device 100 shown in FIG. 1, except thatslanted surfaces 11 s′ are provided instead of the embossment of then-contact layer 11. In FIG. 4, the slanting angle is adjusted to 45°.

The slanted surfaces may have a single slanting angle or differentvalues. In Embodiment 4, slanted surfaces assuming A-plane or M-planeshould not be exposed. Instead of forming an embossment; i.e., theslanted surfaces 11 s′, the entire back surface of the substrate may beprocessed to provide a single slanted surface having an off-angle of,for example, 45° or ≦10°.

Modification of Embodiment 4

In the Group III nitride-based compound semiconductor light-emittingdevice 400 shown in FIG. 4, when a hetero-substrate is employed insteadof the R-plane sapphire substrate, epitaxial growth of a Group IIInitride compound semiconductor occurs in a direction which is not thec-axis or a-axis direction, depending on the type of the main plane ofthe substrate. In such a case, a region where a negative electrode isformed is provided with an embossment which is a surface havingcharacteristics more similar to those of C-plane. Preferably, in somecases, the C-plane-like surface is formed as a slanted surface ratherthan a surface parallel to the epitaxial growth direction. The slantedsurfaces may have a single slanting angle or different values. In thismodification, slanted surfaces assuming A-plane or M-plane should not beexposed.

1. A Group III nitride-based compound semiconductor device producedthrough epitaxial growth of a Group III nitride-based compoundsemiconductor and having an n-type region provided with a negativeelectrode; wherein the n-type region is defined by a surface of ann-type Group III nitride-based compound semiconductor layer formedthrough epitaxial growth and has one or more surfaces which are notparallel to the c-axis and which are formed through etching on saidsurface assuming the main plane other than a Group-III-element-polarC-plane.
 2. A Group III nitride-based compound semiconductor deviceproduced through epitaxial growth of a Group III nitride-based compoundsemiconductor and having an n-type region provided with a negativeelectrode; wherein the n-type region is defined by a surface of ann-type Group III nitride-based compound semiconductor substrate, saidsurface assuming an A-plane or M-plane as its main plane, and areprovided with surfaces which are not parallel to the c-axis and whichare formed through etching.
 3. A Group III nitride-based compoundsemiconductor. device as described in claim 1, wherein the n-type regionprovided with the negative electrode is defined by a surface of thesemiconductor layer assuming an A-plane as its main plane, and at leasta Group-III-element-polar C-plane region formed through etching isexposed to the negative electrode.
 4. A Group III nitride-based compoundsemiconductor device as described in claim 2, wherein at least aGroup-III-element-polar C-plane region formed through etching is exposedto the negative electrode formed on a surface of the n-type Group IIInitride-based compound semiconductor substrate, said surface assuming anA-plane or M-plane as its main plane.
 5. A Group III nitride-basedcompound semiconductor device as described in claim 1, wherein the GroupIII nitride-based compound semiconductor is epitaxially grown on asapphire substrate having an R-plane as its main plane.
 6. A Group IIInitride-based compound semiconductor device as described in claim 3,wherein the Group III nitride-based compound semiconductor isepitaxially grown on a sapphire substrate having an R-plane as its mainplane.
 7. A Group III nitride-based compound semiconductor device asdescribed in claim 1, wherein the negative electrode is provided throughsequentially forming, through vapor deposition, a first metal layercontaining at least titanium (Ti) or vanadium (V), and a second metallayer containing at least aluminum (Al).
 8. A Group III nitride-basedcompound semiconductor device as described in claim 2, wherein thenegative electrode is provided through sequentially forming, throughvapor deposition, a first metal layer containing at least titanium (Ti)or vanadium (V), and a second metal layer containing at least aluminum(Al).
 9. A Group III nitride-based compound semiconductor device asdescribed in claim 3, wherein the negative electrode is provided throughsequentially forming, through vapor deposition, a first metal layercontaining at least titanium (Ti) or vanadium (V), and a second metallayer containing at least aluminum (Al).
 10. A Group III nitride-basedcompound semiconductor device as described in claim 4, wherein thenegative electrode is provided through sequentially forming, throughvapor deposition, a first metal layer containing at least titanium (Ti)or vanadium (V), and a second metal layer containing at least aluminum(Al).
 11. A Group III nitride-based compound semiconductor device asdescribed in claim 5, wherein the negative electrode is provided throughsequentially forming, through vapor deposition, a first metal layercontaining at least titanium (Ti) or vanadium (V), and a second metallayer containing at least aluminum (Al).